Steel cords formed from intertwined steel wires are used as reinforcing material for rubber products such as tires, conveyor belts, and rubber hoses. One example is a stranded steel cord in which a plurality of sheath strands is intertwined around the outer circumferential surface of a core strand (for example, see Japanese Unexamined Patent Application Publication No. 2012-036539A). To manufacture these rubber products, a molded article is formed in which the steel cords constituting the reinforcing material are embedded in an unvulcanized rubber member, after which the molded article is heated at a predetermined temperature and compressed at a predetermined pressure in a vulcanization step to vulcanize the unvulcanized rubber.
In the case of stranded steel cords, the heat of the vulcanization process can make the cords brittle, increasing the occurrence of shearing and leading to a problematic reduction in cord strength. Increasing the diameter of the cord in order to suppress such reductions in cord strength introduces new problems such as increased cord weight and a reduction in flexibility. There is therefore a demand for a stranded steel cord that is capable of suppressing reduction in cord strength caused by the heat of a vulcanization process.